My recent (limited) experiences with your precise situation (*G, no card yet) suggest that YMMVAL (your mileage may vary
a lot):
- United Clubs are no problem. RCCs are happy with your BP, while PCs want to see your card but will accept BP and photo identification.
- Lufthansa SEN lounge at IAD demanded the card, but was willing to accept my signed and stamped mileage printout. I'm skeptical that the CO printable card would have convinced them, but can't say for sure.
- Swiss lounge in ZRH just scanned my BP and let me in -- much to my surprise!
- Maple Leaf lounge in YUL categorically refused to even look at anything other than an authentic plastic card. Literally. As in "No, I won't look at that. We've been getting lambasted by management for letting people in without an official card. You have to talk to United."
Also, ANA Business Lounge at Narita just scanned my economy class BP and allowed me in. (I had by card ready, just in case)