The Gospel According to Luke in Fausset's Bible Dictionary

In the preface to his Gospel Luke refers to "many" who before him had written accounts of what the "eye witnesses" and "ministers of the word" transmitted. This implies the "many" were not themselves eye witnesses or ministers of the word. Matthew's and Mark's Gospels therefore are not referred to in the term "many." But as the phrase "they delivered them to us" (paredosan) includes both written and oral transmission (2 Thessalonians 2:15) Luke's words do not oppose, as Alford thinks, but favor the opinion that those two Gospels were among the sources of Luke's information, especially as Matthew was an "eye-witness," and Mark a "minister of the word." Luke himself applies" minister" (Acts 13:5, hufretees) to John Mark. Luke differs from the "many" in that his work is: (1) "in order," (2) with a" perfect understanding of all things from the first" (pareekoloutheekoti anoothen akriboos, "having traced all things accurately from the remote beginning.") Luke begins with earlier facts of John the Baptist's and of our Lord's history than Matthew and Mark, he writes methodically and in more chronological Order. Ancient testimony assures us that Paul's teaching formed the substratum of Luke's Gospel (the Muratorian Fragment; Irenaeus, Haer. iii. 1,14; Tertullian, Marcion iv. 2; Origen, Eusebius, H. E. vi. 25; Jerome, Vir. Illustr. 7). Compare as to the special revelation to Paul 1 Corinthians 11:23; 1 Corinthians 15:3; Galatians 1:1; Galatians 1:11-12. Paul was an "eye-witness" (1 Corinthians 9:1; Acts 22:14- 15); his expression "according to my gospel" implies the independency of his witness; he quotes words of Christ revealed to him, and not found in the four Gospels (Acts 20:35). Thus, besides Matthew and Mark, to whose Gospels the "many" as well as Luke had access, Paul is the chief "eye witness" to whom Luke refers in the preface. Luke and Paul alone record Jesus' appearing to Peter first of the apostles (Luke 24:34; 1 Corinthians 15:5)...

Link: https://bible-history.com/faussets/L/Luke,+the+gospel+according+to/