The ICL7109 is a very old 2nd source to an Intersil device.
When Maxim was a new company we burned in EVERYTHING to prove our parts would perform to spec.
Later, after we acquired our own mfg facility we burn in only a sampling from each lot, no longer felt we needed to burn in every device.
NOTE: Burn in is stressful to devices and since it is largely unnecessary is seldom performed these days.
The -2 denoted parts which had been burned in.
Parts without a -2 were not burned in.