Historical SPC700 development and Nintendo policy

This is something I've been wondering about ever since hearing about it in maybe 1 or 2 translated Japanese interviews (getting info on what audio work on the SNES was like seems incredibly sparse compared to the wealth of anecdotes available for other systems) and was hoping people here could maybe clear things up.

Basically, what I heard was that if you wanted custom samples for your game Nintendo required you to mail over the samples to them, let them convert the samples to the appropriate format, and then wait for them to mail the processed assets back to you, and that this was very frustrating not just due to the wait but also due to them not always doing a great job with the results.
Is this true and if so, why? The best reason I could think up is that this was a consequence of Nintendo locking down the SNES so hard after the rampant bootleg industry for the NES, so they wanted to make unlicensed development as difficult as possible.

I can imagine this would have killed any semblance of an iterative workflow. You'd basically have one shot at getting it all right, have to plan out everything rigorously and then simply hope for the best.

I could've sworn I'd heard that the devkit had a microphone port to record samples.

It's probably worth asking The Fat Man (George Sanger) how the sound samples were baked or converted.

Might mention it in his book, although I've only paged thru it:
Sanger, George. The Fat Man on Game Audio: Tasty Morsels of Sonic Goodness (Paperback). New Riders Games. ISBN 1-59273-009-4.
Probably available in your local library system?

Bottom line is, the people that would know this are still alive and can be asked.

The BBR rate is documented in Book 1 of the SNES developers manual and thus each company probably just wrote their own tool to do it, or one company made and sold tools for it. Maybe early on it wasn't documented or people would just send data to Nintendo for them to do it rather than invest in their own tools.

Yeah the known documents are of a late version that documents all kinds of things like Super Game Boy and SA-1, so I also thought that interview was from earlier experiences in SNES development, before Nintendo solved the problem by releasing better documents. During the NES days they hardly released any documents at all according to interviews with third party developers as Nintendo initially didn't want any third party support.

I don't know about the sample format, but I read that Sony charged Nintendo a hefty license fee for every released game for using the S-SMP and also sold very expensive development tools for the chip. Maybe they took care of the sample conversion as well at first.

It might be interesting to check this out:
https://assemblergames.com/threads/is-sound-emulator-se-sound-debugger-files.70725/
"disc with driver and programs for SFC/SNES sound development". Seems to be for the IS-Sound or Emulator SE hardware. I haven't yet looked at it myself.

You could also consider asking Ian Schmidt, who did a lot of the sound driver bits for SNES games at Tiburon back in the 90s. I don't think he'd be uncomfortable answering such a question ("did you have to submit sample data to Nintendo to have them give you BSS-encoded results?"). Just be clear/concise with your questions and keep them short.