Now, if you were to look at the datasheets for some slide film - like Fuji Velvia 50 for example, it states to add +1 stop at up to 32 seconds which is well within the range of the control. Fuji Velvia 100 requires +2/3 compensation and the same for Velvia 100f. These are all within the exposure compensation control of these cameras except that only the LX can actually accommodate these extended exposure times past the others limitations.
I am glad you pointed this out as the spec for Velvia 50 states exposure duration of 64 seconds is listed as not recommended while Velvia 100/100f list up to 8 minutes but do not have any other qualifiers as the Velvia 50. May provide some interesting results!