I made some calculations to relate drift angle to groundspeed.
5 deg drift angle corresponds to crosswind well below the 20 k limit for autoland. At a high ground speed of 160 k, 5 deg would correspond to just 13.3 k CW. To reach 20 knots crosswind and 5 deg drift, the GS would have to be 240 knots.! At a "normal" groundspeed of say 145 knots, 5 deg would correspond to 12 knots.
The 5 deg limit seems to be advisory in nature? the extract from Instructor Manual is
"Some requirements are specific to CATIII with NO DH, because an Autoland is compulsory. These are not
necessarily monitored and thus not indicated.
• Incorrect ILS CRS (Δ 5° with runway CRS) leads to incorrect autopilot DECRAB."
The FCOM extract (PRO-NOR-SRP-01-70 P 14/32) merely calls for the PF to "check ILS Course", and does not actually ask you to DO anything about it. Nor does it refer to a limit.
I found a limit in the AFM saying "rudder travel limiter required to be serviceable for autoland with crosswind over 12 knots".
If everyone who flew a Cat III approach and saw a drift angle over 5 deg (how many of us have looked?) went around, there would be a lot fewer landings. I guess that the Instructor Manual is advisory in nature. The decrab not being completed would mean that the aircraft would touchdown with some drift still on. This would mean a landing gear structural limit coming into question. Does anyone have an idea what that is? In terms of drift angle or crosswind limit for landing without decrab, possibly?