As you have mentioned that the thread USB "Not Recognized" on some lot numbers, but fixed by updating cy_boot 5.60→5.70? was locked, we usually lock the thread if there is inactivity. But since you have created a new thread here, we can continue the discussion over here.
Also, there is no need of updating from cy_boot V5.81 to Version 6.0. Both the revisions come with the same changes - "Fixed the defect with IMO trimming with USB on some PSoC 4200L devices." . The only reason between this is, in PSoC Creator V4.2, cy_boot 5.80 was revised to cy_boot 5.81 to fix the issue of defect with IMO trimming with USB on PSoC 4200L devices. But, in PSoC Creator 4.3, cy_boot 5.90 was updated to a newer cy_boot 6.0 for the same purpose.
Hence, both cy_boot 5.81 and cy_boot 6.0 fix the same issue, but cy_boot 6.0 is not supported in PSoC Creator 4.2. Please let us know if this helps or in case of further queries.