Let's look at what's going on:
The DECA signal starts at about 0 dBm, and the SAT tuner chip is rated at -20 dBm, so even though the DECA is out of band, it may still cause the SAT tuner problems.
Starting with the H/HR24, an internal DECA was added. There isn't a BSF, but a diplexer which is doing the same blocking of the DECA signal to the SAT tuner.
An HR20 should either have a DECA installed or a BSF if no DECA is used when connected to coax that has the networking active.
Does it actually damage the receiver, or just cause problems receiving the satellite signal? If you didn't use a BSF where you needed to, is there a risk your receiver becomes a paperweight?