Registrum Gregorii

This collection of 686 letters of Gregory the Great, according to the manuscripts taken "ex registro beati Gregorii", is the largest collection of Gregory's letter and closest to what has reconstructed as the register version of his letters. The letters are divided into 15 indictiones, as the original register was; commonly, it is copied in two volumes with the first containing 393 letters written during the first seven years of Gregory's pontificate (indictiones VII-XV) and 293 letters from the second half of his pontificate (indictiones I-VII), respectively. Ewald refers to complete copies of the Register tradition as R, while his r and ρ refer to copies containing only the letters from the first or second half of Greogry's pontificate.

According to Ewald p. 445, there are seven manuscripts that surely represent the pure (and complete) form of R, plus 25 manuscripts which contain some version of R (including nine incomplete copies). In his count, there are five (or six) copies of r and ten of ρ.

As for mixed versions, Ewald lists seven manuscripts containing ρ and P (Collectio Pauli) (p. 488), one for C + P + ρ (p. 491), five for R + P + C (p. 496), some 20 for R + additions (pp. 499-502), two of a specific version of R + P + C he dubbed "Mailänder Codification" (p. 502), and 18 other manuscripts containing a substantial part of Gregory's epistolary (pp. 506-509)

Ewald, Studien, https://resolver.sub.uni-goettingen.de/purl?PPN345858530_0003