1928 is the year the place opened, and it was the first year they ordered chips (see pictures below). Maybe the black non-denomination chip, of that year, was a prototype to see what the design would look like on a chip, or for souvenirs. A lot of these chips were ordered over the years, so they could change their designs and ideas for chips.

My pages. First link below shows the order cards from USPC.:
http://www.antiquegamblingchips.com/AguaCalienteChips.htm
http://www.antiquegamblingchips.com/AguaaaaaaaTest.htm

Robert

the Agua Caliente, Tijuana, Mexico, resort