The match you want is Dulux Summer Sage (LRV 28), which lands at ΔE 2.1 from Card Room Green. Anything under 2.5 is what we'd call a very close match — the kind of difference you'd only catch if you held the two samples side by side under a daylight bulb. On a finished wall, in a real room, nobody's going to clock it.
The runner-up is Dulux Storm Day (LRV 25.3) at ΔE 3.8. That's a noticeable step further off — it reads a touch greyer and darker, so I'd only reach for it if you can't get hold of Summer Sage or you actively want that slightly more sombre cast. For a true like-for-like swap, Summer Sage is your colour.
Now, the honest caveat. Card Room Green is one of those F&B greens that shifts character through the day — it can go softly sage in good light and lean almost olive-grey when the sun drops. A ΔE figure is measured under controlled lab conditions, so while Summer Sage is mathematically very close, the two won't necessarily *behave* identically across north and south light. F&B's pigment load and the way they build their colours gives a depth that Dulux's trade emulsions don't always replicate at the extremes.
So: get a Dulux tester of Summer Sage and paint a decent-sized patch — A3 at least, two coats — on the wall you're actually doing. Look at it morning and evening before you commit a full tin. If the brand swap is purely about budget or availability, Summer Sage in Dulux Diamond Matt or Trade Vinyl Matt will do you proudly and save you a fair bit per litre over Estate Emulsion.
If the F&B finish itself is what you're after, though, no Dulux match will give you that — that's a different conversation about sheen and pigment, not colour.