hey, this is what I found from the Bride japan website, regarding the compatibility of other aftermarket seats with bride rails.
RECARO MADE
SR Series - RO type / RX type 1 Note
L Series (except electric type) - RO type / RX type 1 Note
AM19 Series Not Wear
C Classic - not wear
CT, CS Series - not wear
D Series - not wear
SPG F-Series
SPGN RO type (Note 2) + INPOTOSAIDOSUTE
SPG pole position RO type (Note 2) + INPOTOSAIDOSUTE
GENUINE RECARO
SR Series RO type / RX type 1 Note
L Series (except electric type) - RO type / RX type 1 Note
AM19 Series Not Wear
AND the only bride rails available for EK are - RO, YO, MO, FG, IG, FX
hope that helps!