Call for information on virtual tape formats 352
I first saw the TPC format in the DECUS tools used to copy sigtapes for distribution up the tape tree. (The tools at the time were BIGTPC for distribute now have been converted to TAP format, because it works with all the emulators without any need for a conversion.
TPC is exactly what you get if you write a RMS-11 variable-length-record file with the records you read from a tape.
The only "funny" is for odd-length records, because of the 16-bit-word-orientation of RMS-11 there's an extra zero byte padded on the end of the record so the next record begins on a even byte boundary. Most DEC-ish tape formats use even-length records, but there certainly are many exceptions even in the DEC world and certainly lots of odd-length records in the larger world.
Call for information on virtual tape formats 353
One matter-of-interpretation is that some DEC OS's (for example RT-11 prior to V5.5 or so) write the tape labels with 512-byte blocks instead of the usual 80-byte blocks when doing...
Another gotcha, not at the container file level but at the ANSI labeled tape level, is that it's entirely legal to have an ANSI labeled tape with two tape marks in a row (for a zero length file) followed by other data. So "double tape mark == end of tape" is not always a good mapping for a tool dealing with tape images.