Some recent releases have had mixes of "long" blocks and "short" blocks. 43 had the standalone Reggaeton track; 42 had the short Latin block and the short Contemporary Rock block (2 songs each); 41 had the short Latin block (2 songs) and the Swing/Jive block (2 songs - and each of those 2 tracks could also be used as standalone tracks too...).
They do a decent job of mixing it up, no?
I never tried the old style of Jam - the first BodyJam ever launched in Canada was #34. It sounds a little haywire though... but maybe sometime I'll get to experience it. I love the long blocks, myself.