Here is an update to the timeline, we use for the Great Crusade, from information given in Tempest.
M30 797 - Emperor launches Great Crusade
M30 799 - Horus is discovered a couple of years into the Great Crusade and is mentored for 3 decades before the next Primarch is discovered.
M30 829 - Leman Russ is discovered 3 decades after Horus.
Between M30 829 and 834 the following Primarchs are discovered:
Missing Primarch A (est 830)
Ferrus Manus (est 831)
Fulgrim is discovered. (160 years before Horus Heresy age of his flagship - would make 845 but order suggests est 832).
Vulkan (est 833)
Rogal Dorn (est 833)
M30 834 - Roboute Guilliman takes control of Ultramarines - Tempest
Between M30 834 and M30 854 the following Primarchs are found:
Magnus the Red (est 839)
Sanguinius (est 844)
Lion El'Jonson (est 849)
M30 854 - Perturabo discovered.
Between M30 854 and 857 Mortarion is discovered (est 856)
M30 857 - Lorgar takes control of Word Bearers - Tempest.
M30 884 - Jaghati Khan discovered. 120 years before Horus Heresy.
Between 884 and 934 - Konrad Curze (est 904) discovered.
M30 934 - Angron in charge of World Eaters for 70 years at time of Betrayer so M30 934. Although he may have been discovered before this but not trusted.
M30 952 - Approx date of Corax discovery (Extermination States he was in command for nearly 50 years at compliance of Indra Sul. Which was around 5 years before Heresy.
M30 963- Monarchia falls and Lorgar goes on Pilgrimage.
M30 964 - Gal Vorbak return from the Eye of Terra and rejoin the great crusade circa 965 as were a year out (40 years before Isstvan). At time of istvaan 3 there was only 47 red WBs inc Argel Tal.
M30 965 - Vlka Fenryka undertake either a Sanction / expunged conflict.
Circa M30 966-967 - Lorgar returns (he was told by Ingathel that over the next 5 decades he would need to recruit another thousand Legionnaires a year, and if one falls to replace with 2 - this means he wasn't in there for a long period of time so he could enact his plan.
Between M30 952 and 981 - Approx date of Primarch B's (est 967) discovery.
M30 969 - Vlka Fenryka undertake either a Sanction / expunged conflict.
M30 972 - The Farinatus Extermination - Night Lords and Raven Guard.
M30 981 - Alpharius takes command of the XXth Legion.
M30 984 - Destruction of Nostramo by the Night Lords.
M30 994 - Isstvan System brought to compliance.
M31 000 - Triumph at Ullanor. Emperor's Children, White Scars, Imperial Fists, Blood Angels, World Eaters, Luna Wolves, Ultramarines, Death Guard, Thousand Sons, Word Bearers, Alpha Legion. Forces - info required. Which Primarchs were fielded during the Campaign?
M31 000 - Chondax Campaign. White Scars.
M31 001 - Council of Nikea.
M31 002 - Kayvas Belt Expedition. Alpha Legion and Blood Angels.
M31 003 - Contact lost with Isstvan system.
M31 003 - Luna Wolves renamed Sons of Horus.
M31 004 - Horus is injured on Davin.
M31 004 - the Destruction of Olympia. Iron Warriors.
M31 004 - The Vlka Fenryka Attack Prospero. Vlka Fenryka, Thousand Sons.
M31 005 - Blood Angels go missing enroute to Signus.
M31 005 - The Dark Angels are dispatched to the Eastern Fringe.
M31 005 - Isstvan III. Sons of Horus, Death Guard, World Eaters and Emperor's Children.
M31 005 - The Ultramarines begin to Muster on Calth.
M31 005 - The Martian Civil War begins.
M31 006 - All data redacted. Have no idea what this can be.
M31 006 - The Dropsite Massacre. Sons of Horus, Death Guard, World Eaters and Emperor's Children, Raven Guard, Iron Hands, Salamanders, Iron Warriors, Word Bearers, Alpha Legion and Night Lords
If you have any further details or information please comment below 😊