The Lionel Lines Caboose No. 6517 was the first offering from Lionel of the bay window type of caboose in 1955. Production of this caboose continued until 1959. During this period there were three variations that were created:
Variation A: There are two lines of underscores of the "BLT 12-55" and "LIONEL" production data. This is the earliest production in 1959. See the above close up illustration.
Variation B: No underscores of the "BLT 12-55" and "LIONEL" production data. Later issues of this caboose.
Variation C: Has a DARKER RED painted body and no underscores of data.