The first 5 letters/numbers for the model of the device, but what after that? is there any guide to understand what exactly they mean by these letters? And why sometimes they repeat the model of the device twice?! and sometimes not!
These 2 firmware names are a good demonstration of (early) Samsung naming conventions.
I8160XXLL2is the "PDA" designator, i.e. build number;
I8160QXXLL3is the "CSC" designator, i.e. baseband version.
There can be multiple CSCs corresponding to a single PDA, released for different regions.
Inside the string:
I8160is, obviously the model number;
XXis for country/region (XX itself means Europe or international);
LL2are the release date and version (within same month): first
Lfor year (L for 2012, M for 2013, etc.), second
Lfor month (A for January, L for December, etc.), and
2for the 2nd version.
Furthermore, you can pinpoint which exact region the firmware is for by using a part of the CSC:
QXE designates the precise region within the one defined in PDA. Match these 3 digits with a list of firmwares (e.g. on SamMobile), and you will know what regions received such releases.