Hmm. I guess I have a question for both you and /u/Dornsinger then - more out of curiosity than anything.
I've kept track of which "Recording Device" is my "original stack", and it looks like the number I had is preserved; the game knows that the "original stack" still has 19 Recording Devices in it (even if in-game, it doesn't "look like it"). My API reports the following in the v2/account/bank endpoint:
{
"id": 87114,
"count": 19,
"binding": "Account"
},
{
"id": 87114,
"count": 1,
"binding": "Account"
},
{
"id": 87114,
"count": 1,
"binding": "Account"
},
//etc, from replacement mails
Where 87114 is the item ID for the Recording Device. So this leads me to have a question: when the item is made stackable again, will the "original stack" once again have whatever the original quantity was? (And were they made unstackable on accident?)