Playing with 'unidentified' fleets in my experience tends to cause more problems than it is worth it (on a free movement game anyway, it can work quite well in a hex system though where you can do things like write down positions and movements until a ship is detected (but even then its STILL much more complicated).
Again not sound like a stuck record but the only game I've played which has GOOD 'unidentified contact' rules in a space miniatures game is, surprise surprise, full thrust (which used a system of contact counters that werent revealed as actual ships other than very general classes (cruiser, frigate etc) until scanned actively or they got close. Of course there were rules for things like sensor decoys or signature amplifiers that could make a frigate look like a battleship and so on. I'll admit to having never actually USED those particular rules as it obviously slows the game down somewhat (at least at first) and only really comes into its own in a campaign where you dont know the size of any of your opponents fleets until you engage them (it CAN be fun in single scenarios but its harder to bluff your opponent when you are playing with x amount of points and your opponent knows this

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