Same as mpeg4, if 47th E Auction may conduct for MPEG 2 and over the slots channels are won then new channels added on mpeg2 there may be Test 517 & 518, hence to complete 5 spots test 114/508/510/517/518.
This is only draft of thinking but It will happen If more participants are win the slots.
Let see next intimation of prasar Bharti for MPEG 2.
And also wait for adding DD National HD in mpeg4.