Ya want the technical answer, or the practical one?
The technical answer: The transfer to your dealer is not complete until he takes possession. At any time up to that moment, the approved transfer can be cancelled and the $200 refunded. Since the transfer is not complete until possession has changed, and BATFE will not process a subsequent transfer until the previous one has been completed, you should wait until your dealer has it in hand before sending in your Form 4s.
The practical answer: BATFE has no way of, or really any interest in, monitoring actual transfers of possession. If your dealer wanted to, he could drive to VT. and wait with your buddy at the mailbox, and drive back to MA. with your MG the minute the F4 arrives.
In addition, you must mail the dealer-to-you F4 to Atlanta where the funds are removed from the package and deposited, and then the rest of the package is forwarded to W.Va. -- not an instantaneous process. So by the time an examiner actually first touches your application, it will be at least days, maybe a week or two, after the previous transfer was approved.
Just make sure your F4 is dated after the approval date of the first one.
BTW, you would have had a tough time holding yer water in the '80s and '90s, when simple transfers took six months at best, usually more like eight or nine months, and one-year-plus was not out of the ordinary.
OTOH, MGs were still
cheap back then....