Even the things that some would tell you are easy to come by - a 31 cm blue jean mou bolide for instance - can involve quite a wait if its not in the store at the moment you decide you want it. A bag is there, and then, its not. All of these bags have some degree of uniqueness - this particular togo birkin may not be exactly like the next "identical" one. So my advice is - if you see something that you like and can see yourself using, ask yourself if you would regret it if you did not buy it and then (1) it was 6 months before you found another one; (2) a year before you found another one; (3) it was discontinued and you never found another one. If the answer is: yes yes and yes - or even no yes and yes - then buy it. Also ask yourself (this is my favorite decision making question by the way): if something else came along that was "better" somehow - color, size, hardware, style, whatever - would regret going with this particular bag. If the answer is yes, then pass.
I hope this helps.
I should get a commission for this.