The revenues of the Bayerische Staatseisenbahnen (Bavarian State Railway) are cataloged in Erler-Jünke's Katalog der Stempelmarken von Deutschland (Catalogue of the Adhesive Revenue Stamps of Germany), Vol. XVII.
In total, there are 52 main varieties, with numerous sub-varieties due to color shades and paper differences.
Here's a general overview --
Stamps of the first set (#1-14) from 1904 have the "Kgl." in the overprint, and are without watermark.
Stamps of the second set (#15-26) are the same, but with a watermark of crossed diagonal lines.

The third set is a single stamp (#27) from 1910, identical to the first set (w/o watermark), but in a previously unreleased value (10 Pf).
Stamps of the fourth set (#28-40) from 1911/17 have the crosses and circle watermark shown by Cjd.
Stamps of the fifth set (#41-52) from 1920 do not have "Kgl." in the overprint, and have the crosses and circle watermark.
Hope this helps. If you'd like to see the relevant listings from the catalog, let me know.