I am afraid but I can't think of any way to get that done.
However, maybe we can try the following -
for games that do not yet have a fixed release date, choose a date way out into the future e.g. maybe 10 years from now.
When listed, the future games will, of course, be listed before the other games. We can easily check if the date falls in that future period and consider it TBD (i.e. not display the alloted date).
Is this idea any good?