I am no expert, but based on lurking here for the past six months or so, it seems that multiple calibers seem to be going through okay. Not putting a specific barrel length or overall length seems to be a reason for Form 1s getting kicked back.
My first Form 1 for an SBR went pending last week. I put one caliber, one barrel length and one overall length on the Form itself, but included an additional sheet of paper which noted that additional calibers, barrel lengths and overall lengths might also be used on occasion, and then basically listed every caliber, barrel length and corresponding overall length I could think of.
The way things seem to be going with approval timelines, I should know within a week or so if my Form gets approved or if they are going to kick it back because of the additional sheet of paper. I will try to remember to update with what happens.
Also, it is not clear from your posts, but it appears that you may have ordered a short barreled upper and an unregistered lower at the same time. If you have an unregistered lower and an upper with a barrel less than 16" in your possession and/or "control" before the ATF has approved your Form 1, you are committing a felony, and could end up doing 10 years federal time and being fined $250,000 (I think that is the maximum fine).
Again, I am not an expert, and I am not sure if you are ordering a lower receiver that has already been "made" into an SBR by the manufacturer (i.e. the manufacturer submitted the required Forms and paid the required tax to make a short barreled rifle as opposed to just a standard lower receiver).
Assuming the receiver you have purchased is not a factory SBR receiver, some here have said that it is okay to leave the upper (or lower if you do not own any other AR-15 lowers) with a friend or family member who does not own an AR-15 lower receiver, and instruct them not to allow you access to it until your Form 1 has been approved. This seems a little dicey to me, but others here have done it. I suppose you could also have your dealer keep the lower until the Form 1 has been approved, as long as you do not own any other AR-15 lower receivers, and this may be what you are planning to do.
The truth is that the chances of you running into any problems is pretty slim, even if you have both the unregistered lower and short barreled upper together before your Form 1 is approved, and a lot of people here will tell you I am making a big fuss over nothing. What you need to ask yourself is whether you want to to take the risk.
Again, I am not an expert, and I am not exactly sure what your situation is. It could be that none of the above is applicable, but I figured it would be better to let you know while you could still do something about it, if necessary.