The 14th is probably a more recent issue. The clutch-back type were introduced in the mid- to late 1950's, primarily to simplify the manufacturing process. The process became standard-issue in the late 1960's or early '70's but there could still be a few pin-backs in the supply system (National Guard and Reserve units that have experienced little or no active duty over the years; for one example)
The regiment has been active since it was first organized in 1861. DI's were first introduced in the early 1920's and only a very few have been redesigned since. This means 14th DI's have always been relatively easy to replace if lost, damaged, etc. Your husband may have bought the chutch-back to replace an original. The insigne is exactly the same, the only difference is the method by which it attaches to the uniform.