With your setting (LA/IR-BLER), they work simultaneously. Normally, an initial coding scheme (or MCS) is chosen for the first transmission. If the decoding of the data fails, then more coding data will be retransmitted (IR) using a lower coding scheme (LA).
I’m not sure if IR is also available for normal GPRS, I have to crosscheck.
Resegmentation and retransmission: When you’re transmitting data, the data is normally divided into smaller ‘pieces’. These pieces are then combined with some coding bits and transmitted as ‘blocks’ (data+coding bits). If you fail to decode a block, you have to retransmit the data with more coding bits. But more coding bits means you cannot transmit the same amount of data per block, thus the data has to be further subdivided. The subdividing is what is referred to as resegmentation, and the retransmission part should be obvious.
Hope you get the idea.