Sorry to be ignorant, but it looks like you all make it too difficult for yourselves ...
To my own experience there is only one golden rule : start with ??? " "
All the existing print's now just work as they did before as long as you respect the normal rules for VFP in attaching the printer (differs for all kind of Win-versions (W95, W98, NT etc) and which is difficult for FPDos-programs (!).
One thing I have to say : we never use ? or ?? for a print, and only Say's. However, I wouldn't know what that differs.
So all of ours prints use only one ??? " " at the beginning and nothing of this kind anymore.
Note that you shouldn't allow VFP (or Win) for any control-sequences but your own. For this matter, we only use our own drivers, meaning that the Say's containing control-sequences are all over the place. With this I only want to say that no matter how complex the "print" is, it doesn't need any adjustment at all, as long as you tell the printer (or whatever is behind it) to operate in raw-mode, and which never should be mixed with the normal "VFP" mode.

Yes, this sounds (too ?) simple, but I think it just is. However, I took a few weeks to come to this for us (many persons working on it).
But again, maybe a ? or ?? destroys things ...