yes basically if you add two publickeys with same X but different Y value (Negative key of each other) exaple:

02f3fad2f7b0f7f5ba634a0618479694b5744091fc7ed53177b5578dba06ee4b77 - 03f3fad2f7b0f7f5ba634a0618479694b5744091fc7ed53177b5578dba06ee4b77

you always get the point at the infinity, so in that case you the value of One of those you can get the value of the other.