This and SSerian are the best answers. If you can find the pins (and they haven't been damaged, moved, etc...) then that works. After that, do it correctly. (I am not a professional land surveyor, but I am a Civil Engineer who works with them routinely).
Land surveyors will typically work off the legal descriptions, plats, and other known monumentation to properly locate your boundaries. It may be done using GPS equipment (in fact likely now) tying into the known locations of other boundaries and monuments.
Late update— I paid for a property line / boundary survey over the summer, cost $500 for my two acre lot. Money well spent. The neighbor behind me, as I suspected, was mowing about 20’ into my property. The surveyor found three corner markers and had to survey / measure off an adjacent property to restake the fourth corner. He planted flags in about 50’ increments all around, so it was impossible for my back neighbor to dispute me taking back and mowing my section of land. He took it upon himself to rip up some flowers and landscaping he’d placed around a tree on my property. Gonna give him benefit of the doubt, probably a mistake on his part.
The side boundaries were about 20’ different than what my side neighbors and I were mowing/assuming were the boundaries. The side I “gained” on is helpful to me as it gives me more room where my workshop is going and is all flat. The side I “lost” on is hilly terrain that goes down into a sinkhole, so no complaints there, just less I have to mow in a rugged area.
Because of how different the survey was compared to what my neighbors and I were assuming, I double checked by measuring stake to stake (my land plat from the county gives boundary dimensions in feet), and it all checks out perfect. Should have done this sooner.