The exterior and cafeteria shots were filmed in an actual prison. Many times while filming the production was halted or rerouted as to allow passage of actual prisoners through shooting areas.
Earl's Inmate Number (#28301-016) is familiar because it is also the Inmate number of Lewis 'Scooter' Libby, Vice President Cheney's staff member who was pardoned in a CIA leak case.
The name of this episode is "My name is inmate #28301-016" but, in the end of the previous episode and the recap at the beginning of this episode his inmate # 1205485 is printed on his shirt. Inmate numbers are not changed from isolation to general population.
The medic who pulls the shiv out of Earl's arm has a medic patch on his lab coat showing the Caduceus, twin snakes entwining a winged staff. The Caduceus started out as the Staff of Hermes and was a symbol of commerce. The single snake entwining a plain staff was the Rod of Asclepius and symbolized medicine. In 1902 some nameless doofus got those two mixed up and mistakenly made the Caduceus the symbol of the US Army Medical Corp. Today most of the USA still gets it wrong, while most other countries get it right.
Glen's prison number is the same as Andy Dufresne's in "The Shawshank Redemption" - #37927