Marlon only wore #18 in 2005, even in spring training. Here is what mbtn.net wrote in February 2005:
Updates (Feb. 8): According to the updated roster at Mets.com:
3 Miguel Cairo
4 Chris Woodward*
10 Ron Calloway
16 Doug Mientkiewicz
17 Dae-Sung Koo
18 Marlon Anderson*
22 Kerry Robinson*
27 Juan Padilla and Mike Matthews*
32 Joe Nelson and Scott Stewart*
52 Andres Galarraga*
Marlon only wore #18 in