"Meniscus" refers to the lenses shape, so it can be one piece of glass with considerable chromatic aberration (simple meniscus), or can be color corrected by using an additional element (achromatic meniscus). When P&S used the term "semi-achromat", I'd guess they were saying that the designer purposefully left some chromatic aberration uncorrected. Gundlach, on the other hand, presumably corrected the chromatic aberration as much as possible.
If using the semi-achromat, it might make sense to experiment in using filters to mimic the color response of the films of the time the lens was designed.
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