Something to note about landing and then using assists and spark cancels to extend your combos..
Yes, doing that will reset your ability to jump cancel, but it also significantly reduces your opponents hit stun
Sure, you can double jump again, but your opponent may be able to recover before you end your combo.
Example with 16.... my bnb has an assist into jlm jc jlm air grab. If i start a combo and assist to extend it and then try that at the end, my opponent will recover before the jump cancelled jlm lands, and the follow up air grab will wiff.
Tl;dr, if you are going to extend combos with assists, shorten your combos after the extension to keep them tight, or make sure your opponent isnt going to recover. Think of it like black beat in GG