Now let's explain in detail what health is ... you should also know the principle of BT, and download and upload it at the same time.
In other words, you are all downloading things from each other's computers ... for example, a file. Now only you and another person are downloading at the same time ... and there are no seeds. You drop to 80%, he drops to 60% ... and at this time, it happens that 20% of his 60% is exactly what you didn't lose ... Your health is at least 100%. Even without seeds, you can finish planting.
On the contrary, if you have 80% and 40% he has no seeds, and his health rate is above 100, you can plant them without seeds ... provided that everyone has turned on BT and connected the seeds.