Designed by Morris F. Benton (and Linn Boyd Benton [Bitstream]) in 1906 and released by ATF in 1908–09 [McGrew], Century Oldstyle has little to do with its predecessor Century Expanded other than its name and proportion. Along with a much lower contrast it has old-style serifs and lettershapes (‘C, G, R’).
Bitstream’s digital version is Century Oldstyle. Adobe/Linotype’s is Century Old Style.