I believe the Pete meers, prior to the Sherlock Holmes series, were all African meerschaum and the system pipe ranges are said to have been carved by Manx meerschaum for some time, but who knows (I have never seen solid documentation of this, so take it for what it is). Peterson's does not have much documentation on this and have used many carvers over the years.
In any event, the meers are extremely hard to date, especially (read impossible) if there are no silver hallmarks - much harder to narrow to a date range than even their briars...
These pipes were available with silver or nickel band, but also available in the classic Peterson shapes with no band (many of those without band were Army Mounts).
The Sherlock Holmes series were Turkish Meerschaum and carved in Turkey, then assembled by Peterson's. The Turkish meer is lighter in weight than African meer, so it is easy to tell the difference.
Without photos it is hard to say whether or not it is a Peterson, but by your stem description I would say that, at the very least, the stem is not Peterson. Often the carvers that Peterson contracted with made shapes very similar to the Peterson shapes with slight changes. This can get confusing as the pipes are easily mistaken for the Peterson versions in the absence of nomenclature, bands or with incorrect stems.
Please do post a photo with closeups of any nomenclature, looking forward to seeing it!