OK. Currently that code looks for a cross reference of specifically “SUBM” (0 @SUBM@ SUBM). I’ll look to see if It can instead look for a record type “SUBM” instead (the second SUBM in the above)
Using a reference of “S0” is not a good idea though, as it will too easily get confused with sources. I suspect that in your tree you will have entries for both of these:
0 @S0@ SUBM
and
0 @S0@ SOUR