Steve P. would be the expert on the chips and how used. My guess is:

In the "old days" of self-dealt 5-card draw, I think the low-limit structure was often:
$1 - $2 limit with a 25c ante (that is, $1 betting increments before the draw, then $2 increments after they draw). The next level would be $2-$4 limit with a 50c ante, and on up to higher levels.

Perhaps that had an ultra-low limit game at 50c / $1 limit and a 12-1/2cent ante, using your chip for that ante?

Also, rather than raking the pot, as with today's house-dealt games, they charged a "time" charge every half hour for each player's seat. (And if you were "walking" at collection time, they would just take the time charge off the top of your stack.)