Difference between CD4017 and CD4017B
Quoting Wikipedia: "The original 4000 series was available in two versions: The A series was unbuffered, while the B series featured buffered inputs and outputs (in the form of additional, simple logic gates). The buffered outputs are able to source or sink more current than the unbuffered outputs, thus eliminating the need for discrete switching transistors in some designs."

I think it's pretty safe to say that the CD4000 number is the generic number, not caring about specific properties like buffered outputs, just the basic logic function. The suffix letter, according to wikipedia, will tell you about the output buffer. Further suffix letters (2nd, 3rd, ... letter) will tell you about packaging options and the like; this may differ from one manufacturer to another and is noted in the data sheet.

Today, only the B versions of the 4000 logic ICs seem to be available. At least that's what the manufacturers' websites tell me. Do you have a link for the 4000 (without B) series data sheet? Is there a manufacturer's logo on the chip?

It might be the case that some manufacturers produce the buffered version (-B), but mark the actual devices without the B. To be sure, you would need a data sheet that tells you the specifics about device marking code.