The display with 16 pins has the 7 segments + DP for each digit, and the 4 commons (12 pins so far.) Then it has a colon and an "upper decimal point", each with both ends on pins (4 more pins.)
The plastics for these displays tend to be standardized, so just because a display LOOKS like it has a colon or decimal points, doesn't mean it actually has LEDs populated in all places. If it's only got 12 pins, it probably doesn't have both colon and decimal points...
I also have in my possession a large number of 4-digit displays (from eBay) where one of the digits has a separate lead for its "F" segment...