Hi, BlueJay. I can sort of answer, but Dick Greenhaus, Susan of the DT or any number of others will be able to give you much mroe info.
Basically the Lyr Add is a prefix we give a thread in which we are submitting lyrics for inclusion in the DT. It helps when Dick and Susan *mine* the threads and gather those to add in throughout the year; they decide what is appropriate. (I don't think Metallica would make the cut!**BG**)
Twice per year, they make a new, updated DT available to us here and for downloading to our home computers, so that you may access it offline also. Dick did just release a new DT, so the next release won't be out until next fall sometime. Anything submitted from the just gone past cut-off time for this new edition, will not be included or found in the DT until then, if they include it.
Hope that is a s clear as mud!**BG**