The PRV is on the regulated side, not the input side, so it's not an issue in this case. If it were to vent under pressure you'd know it
I just compared the parts for their premium
primary and
secondary regulators (pdfs linked), and the good news is the diaphragm and valve "capsule" are shared between the two types.
The bad news is the spring parts are not listed with part numbers. These (all) gas regulators work by balancing spring pressure against gas pressure on either side of a diaphragm to work a small valve (the "capsule"). And as a primary sees the full tank pressure nearly a thousand psi higher than the secondary reg's spec, I have to believe the key is the spring.
This may require direct inquiry to Taprite.
And thanks for the kind words. If I've helped it's my pleasure.
Cheers!