Factory and tube type/batch codes override any printing on the tubes... CCa will have the same code as a 6922/E88CC since that is the tube type; it's just been labelled as a CCa because of the way it tests. (Sections that match tightly, strong test results).
There are numerous ways of figuring out the manufacturer and which factory a tube was made in, if the printing is rubbed off. (Nipple shape, type of getter, what the supports look like for the getter and if they're stamped with anything, amount of flashing on the top of the tube, what the mica looks like, what the grid looks like, inner construction, shape of the glass, etc).
With respect to the A-frame comments above, you'll also see there are various getter shapes (D-shape, O or halo shape in large or small sizes, square, saucer shaped, solid, etc).
Once you can label/identify the parts of the tube, and take a close look at some of the popular brands, you'll find it's fairly straightforward. The factories all seemed to have different fonts as well, so even if you have partial codes, you can normally figure things out. The getter shapes also changed with different years... in general, the D or square shapes are oldest, then O shaped, then A frame for the late 60's/70's. This all depends on the manufacturer of course.
Russian or chinese tubes are probably the easiest to identify, simply by their nipples on the top. The Russian 6DJ8 equivalents also normally always have saucer getters. And the glass is physically larger than others, usually.
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