TR 2750: No mention either way, so the logical assumption would be that it was legal.
TR 3050: As above. Errata for this book mentions nothing.
BattleTech Compendium: As above. Additionally, the Inferno entry for that book specifically allows the use of Infernos in Streak SRM-2s. Though Clan weaponry is present in the book (and thus the Streak SRM-4 and -6), those larger launchers are not mentioned as allowed with infernos--only the -2.
Compendium RoW: As Compendium. Errata for this book mentions nothing.
BMR: Inferno entry now says "Any unit with a standard SRM launcher ... can carry inferno munitions." Carefully reading this entry would make clear that this is a change, in that you can't really argue that Streak launchers are standard launchers (and the Streak entry describes how one works in comparison to a "standard SRM" launcher), but it's subtle enough that I could see many people missing it. Also, the wording is somewhat bad in that it doesn't rule on how you use infernos, but only on how you are allowed to carry them in the first place, though I think you'd have to be pretty munchy to try and argue that with a straight face.
BMR Revised: As non-revised.
TW: Doesn't mention it at all that I can tell, because what a unit can or cannot carry is ultimately a construction issue. Probably buried in TechManual somewhere.
BattleMech Manual: Outrights states infernos are SRM and MML only. In case that's still confusing, Streaks are noted as not being allowed to use any special munitions.
To sum up, yes, 1998 was when the change occurred.