Re: XBLW variants of MCP6001/2 opamps

While hunting for a cheap R-R opamp that's readily available here in
India, I came across the MCP6001 and 6002. Unusually for the Indian
market, a few sites offer several variants of both single and dual types.
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The first three suffix letters stand for temperature range, package and
packing but some have the four extra letters XBLW. These variants for
both single and dual types cost less than a third of the others (roughly
US$0.20 vs $0.75) but I cannot find what the letters stand for. I looked
at datasheets from various sources including the latest one from
Microchip but couldn't find any reference to this extra suffix.
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I assume that the extra letters are not batch or date codes. Chinese
copies maybe??