Review fixes: describe the YEARFRAC, MOD and PERCENTRANK changes in function-parity

docs/function-parity.md

@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (edge cases matched to Excel: base conversions, BITLSHIFT/BITRSHIFT, UNICHAR noncharacters, UPPER/LOWER/PROPER casing, FIXED/DOLLAR output, F/T/GAMMA/WEIBULL/BETA distributions, BINOM trial cap, HARMEAN; earlier: function edge-case parity row; earlier: function edge-case parity row; earlier: function edge-case parity row; earlier: ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; earlier: IMSQRT reproduces the stray real part Excel gives for negative reals) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (YEARFRAC basis 0 February-end rule, MOD quotient limit, PERCENTRANK significance; earlier: edge cases matched to Excel: base conversions, BITLSHIFT/BITRSHIFT, UNICHAR noncharacters, UPPER/LOWER/PROPER casing, FIXED/DOLLAR output, F/T/GAMMA/WEIBULL/BETA distributions, BINOM trial cap, HARMEAN; earlier: ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; earlier: IMSQRT reproduces the stray real part Excel gives for negative reals) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Excel's worksheet functions, category by category, against GridCraft's function library. Part of
 [target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
@@ -150,7 +150,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 | 2026-10-31 | minor | BINOM.DIST and BINOM.DIST.RANGE reject trial counts above 2,147,483,646 after truncation |
 | 2026-10-31 | minor | BETA.DIST density returns `#NUM!` at the lower endpoint with alpha less than or equal to 1 and upper endpoint with beta less than or equal to 1; cumulative behavior is unchanged |
 | 2026-10-31 | minor | HARMEAN returns `#N/A` when array or reference inputs contain no numbers; nonpositive numeric observations remain `#NUM!` |
-| 2026-10-30 | minor | Added a function edge-case parity row. |
+| 2026-10-31 | minor | YEARFRAC basis 0 tests the end-31 rule against the original start day; MOD returns `#NUM!` from a quotient of 1.1259E12; PERCENTRANK returns `#DIV/0!` from significance 309 and 15 significant digits from 15 (Excel 16) |
 | 2026-10-27 | minor | ECMA.CEILING added to the functions that are in our library but not on Microsoft's list (with USDOLLAR), so the counts don't change |
 | 2026-10-26 | minor | IMSQRT uses Excel's polar route with its cosine reduction, so `IMSQRT("-4")` is `1.22514845490862E-16+2i` as in Excel (exact `2i` before); the rows list the IM* differences still open |
 | 2026-10-25 | minor | LAMBDA row: a LAMBDA that calls itself more than 140 times, and a formula nested past the depth limit, give `#NUM!` (#1809; nesting gave `#CALC!` before). `=Foo(1)` where the defined name Foo holds `#N/A` gives `#N/A`, not `#NAME?` |