Yep. Baptized Prots are baptized into the One True Church, the Catholic Church. They may not know it or agree with it or accept it, but if their baptism is valid (Triune with water) then they are members, not formal members, but members nonetheless of Christ's Church.
No one has figured out how they can be restored to a state of sanctifying grace once they've lost it status post sacramental baptism via mortal sin without the means of the forgiveness Christ established so they are in a deficient situation vis-à-vis their Catholic brethren, but its a start at least.
That refers to the OTC in a universal sense, as in particular both RCs and EOs state they are the one true expression of that church, and to hold that Baptized Prots are baptized into the One True Church, the Catholic Church must mean informally. Yet your interpretation is one among others which have been expressed by RCs in seeking to reconcile Lumen Gentium with past statements which excluded all who are not in submission to the pope and in the bosom of the RCC. One said Prots must be converted before death, recanting Prot "heresies. Others interpret CCC 846 as excluding former RCs who "know" that the Catholic Church was founded as necessary by God through Christ," but refuse to remain in it, as referring to formal membership, though i certain do not "know" Rome or the EO is that OTC, but know they claim to be so, but are not. .