The answer about if Ukraine has early or later Su-27 is they have both, the following is for Aircraft painted in the digital paint scheme only.
Jet numbers that have the early tail stinger(Su-27Sm1) 21, 23, 33, 45, 46 and 54 and with the later tail stinger with flare buckets on each side and later type bare metal gun panels (Su-27Pm1) 24, 31, 36, 37, 50, 56, 57, 58, 59, 100 and 101 the above are all painted in the digital scheme with 45, 46, 100 and 101 in the early type with the much lighter shade of medium blue, check your references to be sure on colour. These are all single seat jet