If all you're doing is entering notes, you can probably take lilypond from 15 years ago, run it through the automatic updater, and get your music typeset by current lilypond, using all the improvements made by all the developers since then.
If you have lyrics, they did something 8 years or so ago that the automatic upgrader doesn't deal with, so you have to manually change two or three lines per part to use the current version. This is why there's still a lot of old lilypond on my music publishing site. But it's certainly possible to use 10 year old work with current lilypond.
If you want tablature, someone who actually has tablature may have figured out something better than what I can see. What it looks like from here is:
- Some time in 2003, I spend some time figuring out how I would have to enter Dowland's tablature if that were what I wanted to do. I actually had a measure or two entered, and I got some help writing a scheme function so that it would look more like what's printed in the Dowland facsimiles. I didn't at the time have any real use for the tablature, so I didn't bother entering more than that measure. However, in 2007 I decided a few of the Dowland third book pieces didn't really make sense musically without the lute part, so I attempted to enter the tablature, and found that all the work I'd done 4 years before was useless. I translated the tablature into standard notation, and didn't do anything about having it as tablature.
- This last week, someone from the recorder mailing list offered to help me proofread tablature, so I took a look at what lilypond has now. It would clearly be a fair amount of work to get from the notation I have (for a few pieces) to anything that looks like what Dowland printed, but I found a post on the LUTE mailing list from last year claiming that they had something useful. However, this may have worked with lilypond 2.10, but it no longer works with lilypond 2.12.
Now I didn't spend a lot of time figuring out what has changed about tablature between 2.10 and 2.12, and it could be that it's a trivial problem that just didn't get into convert-ly by accident, and if I wrote a bug report it would get fixed immediately. But since I've done considerable work on tablature over the years, all of which is completely useless with current lilypond, and of course I still have several projects on the website with a fairly tight deadline of mid-October. So I'm not going to do any more work right now. But if any of you feel differently, and do get to where there's useful French lute tablature coming out of lilypond 2.12, please let me know about it.
Meanwhile, I should mention that abctab2ps was already producing useful tablature 10 years ago, and has presumably improved. I stopped using it since tablature by itself is of limited use to me, and there wasn't any way to get from the abctab2ps input to standard notation. But another possibly useful program would translate the tab (plus the tuning information) into ABC or lilypond.