PDP mayhem, GL7500

Is there any pattern to setting up a working PDP context for whatever sim someone puts in these modems?
It seems like sometimes PDP contexts are available to use, sometimes they’re not.

A while back I switched our firmware to use KCNXCFG=3… because using KCNXCFG=1 would fail with a telus card because context 1 was in use by ‘attach.telus.com’.

Now we have customers trying to use Hologram sim cards and in this case the only context that works is 1.

The 7500 documentation says that PDP Contexts 1-5 are reserved for IMS / Verizon / AVMS and that customer applications should use 6-10, but of course none of the AT+K commands support those contexts (just 1-5).

Do we really need firmware that does different things depending on which sim card is in use? All I want to do is set the apn and open a TCP socket…