I agree that the data vendor custom industry classifications are probably more accurate. But the computer generated [fincd12.a] makes backtesting easier.

In the S&P 1500, there are 330 stocks that are classified as Financial Sector by all 3 data sources, and only 57 stocks with disagreement. The new SIP data disagrees with the old SIP data for 29 stocks. The field [fincd12.a] disagrees with the old SIP data for 37 stocks.

If the oldSIP classifications are "correct", then the newSIP Finance Sector classifications are "wrong" for 29 out of 387 stocks, and [fincd12.a] Finance Sector classifications are "wrong" for 37 out of 387 stocks. Not much difference, and a less than 10% "error" rate.

For example, placement in the Financial Sector:
ABG Asbury Automotive Group: only [fincd12.a]
FDS FactSet Research: only newSIP
WU Western Union: not oldSIP
WT WisdomTree: not [fincd12.a]

newSIP is SIP 20241017 data with Sector "60 - Real Estate" or "40 - Financials".
fincd is GTR1 20241017 data with fincd12.a = 11
oldSIP is SIP 20240930 data with trbc2 = 60 or 55.

newSIP  fincd  oldSIP  count  tickers
  0       1      0       17   ABG, ALLE, CAR, CI, CNC, CRVL, CVS, CXW, ELV, HRB, HUM, MOH, PLUS, RGLD, SCI, TPH, UNH
  1       0      0       19   CPAY, DFIN, EVTC, FDS, FI, FIS, GPN, JKHY, JXN, MA, MCO, MSCI, NATL, PAYO, PRG, PYPL, RDN, SPGI, V
  1       1      0       8    BRK-B, CSGP, CURB, EEFT, MORN, SITC, WEX, WU
  0       0      1       1    GATX
  0       1      1       1    GEO
  1       0      1       11   ALEX, ALLY, BFH, CG, MMI, NAVI, NMIH, ROIC, VIRT, VRTS, WT