Is Train ticket bought at the Basel station train specific?

So you're attempting to purchase a ticket on the TGV to Paris CDG? Yes, it will be a train specific...especially if it says nonrefundable. Yes, there is a real ticket counter at Basel SBB

Oh yes - a definite disaster. ALWAYS spend the night before you flight in the city where your flight originates.

Difficult question because Basel is served by 3 rail companies, SBB, SNCF and DB (Swiss, French and German) with different ticket rules.

• Interlaken to Basel is SBB. Normal SBB tickets are not train specific, they are valid on any train on the date shown on the ticket. There is also no discount for advance purchase, just buy from the ticket machine.
• Basel to Strasbourg and Strasbourg to Charles de Gaulle is SNCF. Here it depends on which train type.
• Basel to Strasbourg an "RER" (regional train, even though it runs at 200 Km/Hr). Again this is no reservations, sit anywhere and travel on any train.
• Strasbourg to Charles de Gaulle is a "TGV" (High Speed train). This you MUST buy in advance. Tickets are cheaper the earlier you buy. Tickets are for a specific seat, seat number is listed on the ticket.

1) If you miss a connection because an incoming train is late, yes you can use the next train. If you miss it because you wasted time, no.
2) Trains to Strasbourg depart from an annex (platforms 30-35). Currently, because of building work, to access these from the main station you need to go out the main entrance and along the street for ~200 metres. It is signposted, but allow extra time.
3) There is a ticket office at Basel, it is a very big station (20 platforms). Beware, SBB ticket machines only sell tickets to SBB destinations. You would need an SNCF machine (in the annex), or the manned ticket counter.

Finally, I would not recommend travelling that far prior to a flight. Too many risks.

There are a few TGVs per day running directly from Strasbourg to Charles de Gualle TGV station, rather than going into central Paris. That's the ticket that offers the most savings with advance purchase, that requires a reservation, and that can sell out, so that's the portion to book ahead.

The trains legs inside Switzerland and from Basel to Strasbourg can be easily purchased there at any Swiss station or perhaps you'll have a Swiss Travel Pass that would cover you as far as Basel. If train schedules suggest that you depart Interlaken at 10:05, for instance, to catch the 14:59 departure from Strasbourg, then you could certainly choose to leave Interlaken earlier.

I want to thank all of you for the great help and advice. Just as FYI, we were looking to leave Interlaken West on the 5:05 am train to Basel, using our Swiss Travel Pass, then transferring at Basel Sbb to the train to Strasbourg 7:17, we have already bought our ticket from Strasbourg to CDG on TVG train leaving at 9:59 arriving in Paris at 12:06 pm, our flight leaves at 5:49 pm. Our main concern was, should we buy the ticket online from Basel to Strasbourg or waiti till we arrive on our river cruise in Basel. We could buy in person and map out our route for our departure to familiarize ourselves with the station or any construction issues, and if we bought in person and missed the 7:17 train use the same ticket for the next train.
Again wonderful people A Big Thank You!

Are you saying you will be in Basel on an earlier date? If so, you can buy the ticket then. Or you could buy online.
I would not leave buying the ticket until your stopover between trains, purely for the reason you don't want to waste 10 precious minutes when you have a train to catch. Personally I would have bought Basel - Strasbourg - Charles de Gaulle as one purchase, simpler and possibly cheaper than buying separately.

"if we bought in person and missed the 7:17 train" - yes, but you would then presumably miss the TGV at Strasbourg, which IS a train-specific ticket. Tickets for the TGV are only valid on a later train if your previous train was late, NOT because you dawdled or got lost.

"we have already bought our ticket from Strasbourg to CDG on TVG train leaving at 9:59 arriving in Paris at 12:06 pm," _ I thought you were going direct to Charles de Gaulle, NOT via Paris.

First train of the day from Interlaken West is 05:03 (NOT :05, it will be gone at 05:05) arriving Basel SBB 06:59 (I looked it up).
Then 07:21 depart Basel, 08:39 Strasbourg. That gives you plenty of time at Strasbourg for a 09:59 departure. But 06:59 to 07:21 is less time in Basel, where you have a 10 minute walk involved.

And 05:03 is disgustingly early!

Thank you, Chris, yes the time is super early out of Basel, but we will have a 9 hr flight on our plane, where we will get some sleep. And that will give us 1 extra day in your beautiful country. And we are definitely taking your suggestion of buying a train ticket when we first arrive in Basel. We were not sure whether leaving a day early out of Basel and spending the night in Strasbourg just to get closer to CDG, which we have the TVG directly to. That is why we did not buy a combine ticket Basel, Strasbourg together. We are not stopping in Paris, but to CDG. If all goes well we arrive at 12:06 leaving us with over 5 hours to our flight. We are also trying to make sure no strikes are in the works for May 9, which is the day we leave Strasbough to CDG. I found a France Train sight that gives information, in March, 2019, 2 stricks will be happening. If so we will have to have to get a back up plan.
Again, thank you for your help!