As lots of the old engraved chips were produced 100 years ago (or more), the dies were almost certainly engraved by hand. Note that the classification of "engraved", vs inlaid, or embossed, etc., is a little misleading as what is engraved is the metal die that is used to put the design on each chip, and not the chip itself.

In the old days, anyone with the time and money could produce poker chips of any design they wanted. In most cases, my guess that chips like the horseshoe design that are similar but not identical, are from different chip makers. Another possibility is the same maker re-engraving dies after the original metal die wore out or broke.