It's hard to tell what exactly the problem is without the MIB text and access to the device itself. Plus you've said some indexes return expected results and some don't - adding to the confusion.

One of my earlier posts (Re^3: Where is the bug in this Net::SNMP code?) shows example code for pulling out tabular objects of a printer MIB. Another even earlier post (Re^3: SNMP from script conflicts with snmpwalk) discusses issues to do with reading tables and ensuring all objects in a table align.

I've never used get_table myself, it's a relatively new function introduced into Net::SNMP. If you're unsure exactly what the behaviour is of your code then doing it the hard way (like I like to do) may be your best option so you can easily debug.