I am just another user, so not an authority. I am guessing that it would not be a bad idea to attach the 592-B.  Be sure to mark the NO button for Send PDF attachment with federal return.  

I find it interesting that the diagnostics  page https://proconnect.intuit.com/community/individual/help/ca-diagnostic-ref-15323-credit-for-backup-wi... makes a link with another software filing service. 

FTB 540 Instructions state: 

"Claiming withholding amounts:

• Go to ftb.ca.gov and login or register for MyFTB to verify withheld amount or see instructions for line 71 of Form 540. Confirm only California income tax withheld is claimed.
• Verify real estate or other withholding amount from Form 592-B, Resident and Nonresident Withholding Statement, and Form 593, Real Estate Withholding Tax Statement. See instructions for line 73 of Form 540." 

AND

"Line 73 – Withholding (Form 592-B and/or 593)

Enter the total of California withholding from Form 592-B and Form 593. Attach a copy of Form(s) 592-B and 593 to the lower front of Form 540, Side 1.

If your filing status changed after escrow closed and before filing your California tax return, please contact us at 888-792-4900, prior to filing your California tax return, for instructions on how to claim your withholding credit.

Caution: Do not include withholding from federal Form(s) W-2, W-2G, or 1099, or NCNR member’s tax from Schedule K-1 (568), line 15e on this line."