Jtdcftul

When I was taking harmony theory my teacher would take points off for using enharmonic notes in a chord definition. He'd say D# is the sharp ninth of C, not Eb. And he is (was) correct. There is good reason to follow the correct theoretical naming convention. I also find it easier to sight read when the notes are in the correct chord form.

I have noticed that several open source music writing and tab programs will NOT place notes where I want them. Perhaps the option is there and I just don't know how to use it but I suspect that if it isn't obvious a lot of folks are going to ignore it. Hopefully this is a technology issue and not a lowering standards issue. Since every Tom, Dick, and Harry, can write and publish it's hard to know if you are referring to professional publications or junk you are finding on line. Perhaps you could make your question better by offering a few examples.

Some of it may very well be ignorance. Perhaps a young musician with little formal education is posting work and is not aware of the meaning behind the note names.

As for your last question, does it matter? I really think it does. For one thing enharmonic tones are a feature of equal tempered tuning and not in Just tuning. There is a real loss if information. The movement of notes will not appear correct. And it will be difficult to identify chords properly when sight reading, at least for guitar and I suspect piano too.

Most composers I know operate on two levels: theoretical and practical.

The difference between A and Bbb only matters for analytical purposes. When reading melodically double-flats and double-sharps can be difficult for performers to read because they lead to more diminished and augmented intervals (like G to Bbb, or Bbb to C) - which composers try to avoid notating.

The last step of the composition process for many composers is to go through each instruments' part and review it for readability. So, for instance, if a line goes Gb-Bbb-C, they will change that Bbb to an A because it will be clearer to a performer.

I don't necessarily think it's because the writers are lazy or ignorant of theory. It's the composer's job to convey the notes clearly to the performer, not to give them a theory lesson.

It may be erroneous and the smartest thing to write at the same time.
Consider film scores, here a piece in any key will often be written without any sharps or flats at the key signature. It would look like it were considered in C maj or Amin, wich may be utterly untrue, but it makes practical sense: Musicians read it easily and do not miss as many flats / sharps by accident. Is it "correct" ? Probably not.

I like writing my stuff in the correct way, but sometimes I will change it in for practical reasons... If one analyzes it, he will find out soon enough. But yeah... my guess it is lazyness, and giving in to lazyness, time pressure and so on...

My feeling is that these mistakes are made when the writer isn't used to reading the staff or doesn't understand the harmonic implications of enharmonic spellings.

...does it really matter?

I say it matter only if you want to be able to refer to chords by letter names and accidentals and if you want to consistently describe relative relations of tones and chords.

The point can be illustrated by pushing things to the absurd. How about a circle of diminished sixths? Or a C major chord spelled Dbb E Fx? Those would be obviously silly to even the beginning student.

It shouldn't be too hard to go from that beginner level to explain why F A C D# resolves in Am as Gr+6|i6/4 V functioning as an inverted, altered subdominant, but F A C Eb resolves in Bb as V7|I functioning as a dominant, and the difference is implied by the enharmonic spellings even though both chords in isolation sound like dominant seventh chords.

When people write Co7, spell it C Eb Gb A, and then resolve it to C# major they need to be corrected... on both errors!

It's totally unacceptable in educational materials.

You've already answered your question: some notation may be ignorance, some in purpose to make it easier for reading.

But there seems to be another reason: toward a modern notation!

as they speak about traditional notation there must be a movement to change things:

http://musicnotation.org/tutorials/enharmonic-equivalents/

It says:

„Various Approaches

There are at least three different approaches to the representation of enharmonic equivalents in chromatic staff notation systems:

1. Not Explicitly Differentiating Between Enharmonic Equivalents
   …while assuming twelve-tone equal temperament for intonation and/or relying on contextual cues and conventions for harmonic/melodic function and intonation.“ ...

and:

These approaches involve nomenclature as well, since the traditional note and interval names make a distinction between enharmonic equivalents. For example, the first approach above lends itself to using a novel nomenclature for notes and intervals, otherwise the names of some notes and intervals would remain ambiguous.

„To conclude, there are different views on just how important it is to distinguish between enharmonic equivalents in music notation, and on how not doing so might affect the understanding of their intonation and tonal function. Fortunately, there are also corresponding approaches to representing them (or not) in a chromatic staff notation system.„

Many jazz arrangers will substitute B for Cb, even when it's the b7 in Db7 or the minor third in Abm. It sends me mad, but it's the convention in that style. They'll spell a dim7 chord whatever way avoids a 'difficult' accidental.

It's very common in printed song copies to see a diminished 7th chord mis-spelt, in fact it would be quite remarkable to see Cdim7 spelt with a Bbb. This doesn't worry me in the slightest!

In the 'classical' and academic worlds you're more likely to see one spelt 'correctly'. But would you fault Beethoven for this? Why not?