I went to
T-Rank and looked at the ADJDE (Adjusted Defensive Efficiency) column. It is, indeed, #18 "since the start of March", but why confine it to such a tiny stretch of time? Duke is #21 over the whole season so far, which should be more meaningful.
Also, while I have personal weaknesses in the fields of both statistics and memory, I seem to remember DBR concerns about our defensive rating back in 2015, as the team worked their way toward a title. You list them as #11, and that is in fact their ADJDE rank over the whole season, but that squad was #46 at the end of February. It moved up to #11 because they had the #3 defense over March and April. I think someone kept track of their defensive ranking game by game, as the team kept winning. We can re-create it here:
#39 Start of ACC Tournament -- March 10, 2015
#33 After ACCT Quarterfinal Win
#32 After ACCT Semifinal Loss (same on Selection Sunday)
#31 After NCAAT First Round
#24 After NCAAT Second Round
#19 After NCAAT Third Round
#17 After NCAAT Fourth Round
#16 After NCAAT National Semifinal
#16 After NCAAT National Championship -- April 7, 2015
Huh. For whatever reason, T-Rank moves Duke up from #16 to #11 on May 1, nearly a month after the season is over. (It's still #16 on April 30.) The site has a default date setting of November 1 to May 1 for each season, so it's going to say #11 even if maybe it isn't.
That #21 ranking for this season is also a lie. If we keep the season start date of November 1, 2022 but change the end date from May 1, 2023 to today, Duke is ranked #25.
Anyway, if we measure Duke's ADJDE ranking on Selection Sundays, we get the following.
2023: #25
2022: #39
2021: #84 (not selected to tournament)
2020: #10 (tournament cancelled)
2019: #5
2018: #14
2017: #37
2016: #74
2015: #32
2014: #58
2013: #29
2012: #61
2011: #3
2010: #5
Duke's OAD era starts in 2011, but I threw in 2010 for the fun of it. On past Selection Sundays, compared to today, Duke had a higher rated ADJDE in 2010, 2011, 2018, and 2019, and slightly lower rated ADJDE in 2013 and 2015. With the Sweet Sixteen exception of 2011, it's interesting that Duke at least made the Elite Eight in each of those NCAA Tournaments.