The year of 1906 was when Lionel dropped the 2 7/8 scale trains, and started to produce what is now "Standard Gauge", which they quickly trademarked the name. Both the #5 & #6 were produced in 1906 with matching 'square tenders. That same year Lionel produced the #18, #19, & #190 passenger cars. These were produced from 1906 until approx. 1923.
Referencing Dave McEntarfer's book on Sets, the first Set was made in 1915, with the consist of #6 loco/tender, #18 Pullman, #19, Combine (Pullman & Baggage car), & #190 Observation Car. The Set was #620, and the only one listed as a Set made in 1915. There is nothing found with regard to the #1910 car ever being used with the #6 loco, and it didn't appear until 1910, well after the #6 loco was introduced. Chances are that there were or are other undocumented sets using the #6 with the 18, 19 & 190 consist.
This is from the McEntarfer book plus the TCA Standard of the World books.
