Actually, I have seen 16 in use (0 through 15, using the tabernacle for both).
In any case, we live in a dynamic world. God did not come down from heaven and say “You will have 14 Stations of the Cross, and this it what they’ll be.” The devotion was a human invention, and as with all human inventions it evolves and changes over time. We are just in that process.
From the old Catholic Encyclopedia:
With regard to the number of Stations it is not at all easy to determine how this came to be fixed at fourteen, for it seems to have varied considerably at different times and places. And, naturally, with varying numbers the incidents of the Passion commemorated also varied greatly. Wey’s account, written in the middle of the fifteenth century, gives fourteen, but only five of these correspond with ours, and of the others, seven are only remotely connected with our Via Crucis…
…When Romanet Boffin visited Jerusalem in 1515 for the purpose of obtaining correct details for his set of Stations at Romans, two friars there told him that there ought to be thirty-one in all, but in the manuals of devotion subsequently issued for the use of those visiting these Stations they are given variously as nineteen, twenty-five, and thirty-seven, so it seems that even in the same place the number was not determined very definitely. A book entitled “Jerusalem sicut Christi tempore floruit”, written by one Adrichomius and published in 1584, gives twelve Stations which correspond exactly with the first twelve of ours…