Tell me please, in the name of the lineup 4, 5 and 6, for example Bluecore-4, Bluecore-5, Bluecore-6, is taken from the MCU XAP4, XAP5 and 6 respectively? Suspicious coincidence. Where can you read about this?The figure in the name is taken from the name of the microprocessor. I'm just not sure that it's XAP4 in Bluecor4.
Unless this is documented in the product datasheets, any answer is probably guesswork. As a first assumption, you might be right - but this is a prime example of why you need to refer to datasheets for a product (and also link them in your questions).
Generally, no there is no rule that one product namespace needs to relate to the namespace of a different product. 'Clever marketeers' take advantage of this type of assumption some of the time. This is especially the case when talking about a SoC built up from various IP elements from different companies.