Do you have a source for them being indistinguishable when administered intravenously? Because I personally do not think that is the case, no bell ringer with ritalin and it lasts longer too, also slightly less euphoric. Only thing in common is the stimulation feels the same and the general vibe, but there are many differences....definitely not indistinguishable
edit: I think I managed to find the source for that info on my own, interesting read, however there is no mention of them being indistinguishable really..."MPH self-administration resulted in nearly identical changes in behavior." doesn't necessarily mean they are indistinguishable