I think if Zhu Tianxi in fact has another complete Luohan system learned from Shi Degen separate from Liu Zhenhai's, then that would show Shi Degen had two different yet related Luohan systems (different students of Shi Degen testifying Liu's as Degen's 18 road system). It may well be a Xiyuan & Nanyuan situation as RDH said is possible.

I know Shi Zhenxu had some Luohanquan, but nothing I've seen/learned is outside Liu Zhenhai's material and the 8 road "Luohan Shiba Shou", as far as boxing sets. We do have a rare Luohan partner set and a very rare bead set that is unmistakably Luohan, with full-lying 'sleeping arhat' postures, which I have seen nowhere else. Both of these were revived just a year and half ago.