Lisa,
The whole point is that a remedy does not have to fit every single symptom that you have. This is not the idea. The idea is that you get the 'similimum', which actually means the best matching remedy, but it does NOT have to match everything. If it does, then this is Isopathy and not homeopathy.
Sometimes a homeopath will get a partial similar, which is similar but not the similimum. This will still do something until and similimum can be found.
This is why it is very important to take a very good and full case from a patient and is why we spend a lot of time doing this. This is also why you must analyse a case too and by doing all this, you can then come up with the best remedy.
This is exactly why homeopathy is a lot more involved than people think and why homeopaths have to train for at least 3 years and possibly 4 years part time to be able to do this properly.
Also, although I live in England now, I was originally born and brought up in South Africa and trained in homeopathy there. Homeopathic training in South Africa is a 5 year full time course that leads to the award of a Masters in homeopathy. These courses are undertaken at the Technical Colleges out there and they award the qualification of MTech (Hom).
The child with croup was treated with Carcinosin first of all. Did very well on this in various potencies. The 'constitutional' remedy was Phosphorus and the child is now better having been given this remedy. The croup was treated constitutionally and at times during constitutional treatment, an acute remedy is given to hold in a lower potency to treat any attack that may occur. This acute remedy may be different from the constituional remedy, but will fit the acute picture.
The snake and the spider remedies have a lot of heart pathologies and when a person has quite severe pathology it is perfectly acceptable to treat at a pathological level rather than a constitutional level. What you can do is just prescribe on the physical symptoms only and give that remedy in a lower potency specifically to treat the pathological layer. All remedies have physical symptoms as well as the general and mental/emotional symptoms.