The submarine-steel question and the extra-Astute timetable

When did the US submarine-steel quality issue become known, and how does it relate to the proposed extra British submarines?

The 2020s is the date given, with Britain using a different steel source; this does not explain the earlier extra-Astute construction opportunities.

Recognition of the US steel problem is dated to the 2020s in this discussion, with British submarines said to obtain their steel from a different source. That timing would be too late to explain the earlier extra Astutes proposed for the counterfactual. The discussion returns to possible British starts in 2015, 2017 and 2019 and the need to leave room for Dreadnought construction. It does not establish how many American boats were affected or quantify any reduction in service life.