more detailed clarification on [a1] dumps?

I just found my very first (U) [a1][!] dump (Micro Machines 64 Turbo) and now I'm wondering more about this type of dump.
I know officially it stands for:

: [a] This is simply an alternate version of a :\
: ROM. Many games have been re-released to :\
: fix bugs or even to eliminate Game Genie :\
: codes (Yes, Nintendo hates that device). :\

If this is the case why isn't it just a (U) (v1.1) [!] dump or similar? The wording of "alternate" doesn't make much sense to me here. If it really has bugs fixed (or otherwise altered code) it's a different version no alternate (should differ only in non-relevant issues like internal romname or whatever) one.
Isn't according to this an [a] dump always preferred to non [a] dump? I don't care about Game Genie but I'm interested in bug fixes.... (but of course not if the "fix" is a change in blood color from red to green like in Zelda:OOT v1.2). But I guess in the worst case a new microcode (unsupported by the emulator) is used in the fix.

Comparing a dump of the same rom in both [a1][!] and standard [!] versions in more detail might be very interesting.

blizz said:

the [a] are not alternate game versions they're just the same game dumped by a different person, just an alternate dump of the same game.

Click to expand...

So what's the byte difference between the 2 versions exactly? They have obviously different CRCs so there must be *some* difference.
If we both were to use the exact same backup station and dumped the exact same cartridge using the exact same method... Or if you were to dump the same game twice with the same method...
Would the dumps be identical?
At least this is what I would expect/hope.

It doesn't make much sense to store timestamps / unique ids in the dump to make it unique now does it?