The Dato was always easy to get with a good discount and that's why the secondhand value was or is not that great.
If AP or Panerai would make limited editions in series of 10.000 pieces instead of a few hundred to max 2 K they would also drop in value
the 5070 was made in pretty small numbers, much less than what Patek could sell.
Why does a PAM 111 go 35% under list and a LE like a 339 / 382 / ... doesn't ... same reason as the Patek 5070 vs Lange dato. --> being 'more than enough pieces and not enough pieces to supply the market
The Dato is made in too many pieces
But this can't be compared with a Vintage Panerai that rose 1000 or 2000 % in 15 years, that is insane
5 % per year like your exaple the 5070 is imo very acceptable and still 'safe'
If a vintage Panerai would go from 6000 in 1995 to 14000 in 2012 I wouldn't call it crazy .... but 100 K ??????