Accidentals - What the heck!?

[xvimbi]

There are a couple of recent threads about accidentals, an easy enough subject, or so one would think...

The question is about the applicability of accidentals. What is correct?

a) when there is an accidental in a measure, say A#, any subsequent A's in that measure, no matter what octave they are in, are also sharped

b) "The sign applies only to the line or space where it first appears; if the same note appears in another octave, or, in the case of multi-staves scores on another staff, the accidental must be restated ... Contrast this with the rule for signs appearing in the key signature which apply to all relevant notes in any octave on the stave."

Answer b) has been pointed out to me my Abel88 in another thread, which resulted in utter disbelief on my part, but I thought I'd research the issue a bit. So, I stumbled into a popular website on music theory, where the above statement b) has been taken from:
https://www.dolmetsch.com/musictheory9.htm (scroll down to "Using accidentals")

Now, I have been raised and bred with the notion that statement a) is correct. I have also asked around a bit, and so far everybody (including some very experienced musicians) was under the same impression. So, has there been a change in rules that I have missed? What gives?

[bnatural]

There are a couple of recent threads about accidentals, an easy enough subject, or so one would think...

The question is about the applicability of accidentals. What is correct?

a) when there is an accidental in a measure, say A#, any subsequent A's in that measure, no matter what octave they are in, are also sharped

b) "The sign applies only to the line or space where it first appears; if the same note appears in another octave, or, in the case of multi-staves scores on another staff, the accidental must be restated ... Contrast this with the rule for signs appearing in the key signature which apply to all relevant notes in any octave on the stave."

Answer b) has been pointed out to me my Abel88 in another thread, which resulted in utter disbelief on my part, but I thought I'd research the issue a bit. So, I stumbled into a popular website on music theory, where the above statement b) has been taken from:
https://www.dolmetsch.com/musictheory9.htm (scroll down to "Using accidentals")

Now, I have been raised and bred with the notion that statement a) is correct. I have also asked around a bit, and so far everybody (including some very experienced musicians) was under the same impression. So, has there been a change in rules that I have missed? What gives?

Intuition tells me a) is correct.  However, I was trained in my theory class that b) was correct.

Any formal training in music indicates otherwise would be a telling sign of the quality of the teaching.

Again, the correct answer is b).

You may feel the earth is flat, but the truth is otherwise.

[pianonut]

it is my understanding that a) is correct   BUT, now that i have looked up 'accidental' in the harvard dictionary of music, it says b)"remains in force for all notes OCCURRING ON THE SAME LINE or SPACE in the remainder of the measure.  

thanks for asking this question because i am working on barber's nocturne and kinda got mixed up on that myself.  some places you do wonder what the composer really meant.  did he make a mistake, or did he mean to have two separate things going on with the notes.

[allchopin]

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