I have no horse in this race obviously and not trying to stir the pot, and apologies if I'm speaking out of turn, but as a collector and seller myself, I'm a bit of a tag junkie and I do honestly believe the Nirvana shirt to be a later modern-ish reprint. The examples you had of double-tag Hanes shirts were later reprints, and in my experience the double tags in general are 1998/99 and later. The Jerry Garcia shirt I know my deadhead cousin bought in 1999 from a head shop (I remember it because I thought it was ridiculous and he wore it for the first time to my high school graduation), it's the same shirt and definitely had the same copyright date because he still has it and wears it occasionally but the tag is long gone. And like some of the later Metallica reissues with Hanes double tags or other tags, they maintain the old copyright date because they're using the same art. There's no hard and fast rule for this, but a lot of bands or merch companies have done this in the past and it caused confusion for lots of people. It even happens with Snoopy shirts on a 90s Artex or Jostens tag and saying "vintage 1964 Snoopy Shirt" or something because they used the 1964 copyright of Peanuts itself, rather than the print production year for some reason.
The hot rod shirt would appear to be a smoking gun as far as print date and tag match, but I would say it's more likely that the driver did that art and originally printed in 1993 and continued printing it for a long time after to sell at rallies and what not (very common in that world). In fact, just out of curiosity I Googled it and found that an automotive website is still selling shirts with this same exact design in sizes S-XXXL so it's definitely been in print recently. Can't make out the copyright date from the photo but it appears to be the same as the link to the one on ebay. Here's the shirt on this website: http://www.kramerauto.com/proddetail.asp?prod=z01-01
For the Jerry Garcia shirt there's a lot of them in circulation. And in my experience the Winterland copyrighted shirts from 1993-95 were for the most part printed with Winterland tags. The later reprints were Hanes or other brands, early-late 90s were the single tag Hanes made in the USA. The much later reprints (98/99-present) were always double tag Hanes or other brands, usually made elsewhere, or at the very least assembled in Mexico, Haiti, etc. Hanes definitely used that distinctive arrow logo in the mid-late 90s but the double tag for sure wouldn't have been around in 1993.
In my opinion this would be the timeframe for the Jerry printings:
Original 1993 Winterland Tag - http://www.ebay.com/itm/Jerry-Garcia-Gr ... SwXAJYWAtm
Early-late 90s reprint - http://www.ebay.com/itm/Vintage-Jerry-G ... Sw2xRYTK7R
1998/99-present reprint - http://www.ebay.com/itm/Grateful-Dead-S ... Sw4GVYSZbs
The Primus and Mel Tillis you're dead on about with the era matching the year on the shirt, but like I said those are single tag Hanes and made in the USA with no qualifiers. So those would have been early 90s for sure.
And that's why I think the Nirvana shirt in question isn't actually from 1993. This seems like a one-off modern day head shop bootleg reprint more than anything since there aren't any other matching examples in the wild. And the official tour shirts from that year have a slightly different front print and also have the back print with the cities, and the two that are listed now have a Delta tag and a Screen Stars Best tag which would be period correct. I could be wrong, feel free to correct me. Like I said, I hope you don't take offense to this but I've been reading this thread and I do feel the era is off for sure on the Nirvana one based on what I know from collecting for the last 20 years and selling on and off for a decade or so.