diff --git a/docs/nixos_build_spec.md b/docs/nixos_build_spec.md
index 5b5b338..c507300 100644
--- a/docs/nixos_build_spec.md
+++ b/docs/nixos_build_spec.md
@@ -9,6 +9,16 @@ Target disk: /dev/nvme0n1
 - Sector size (logical/physical): 512 bytes / 512 bytes
 Install target is NVMe only. Do not select /dev/sdX devices in the installer.
 
+NOTE: GPT partition table entries may not be stored/printed in on-disk (Start sector) order.
+- Do NOT rely on the order shown by some tools.
+- Always identify partitions by (partition number + type + UUID/label).
+- If you need the physical order, sort by the “Start” sector column (e.g. `fdisk -l` output).
+
+Verification commands (run before formatting):
+- `lsblk -o NAME,SIZE,TYPE,FSTYPE,LABEL,UUID,MOUNTPOINTS`
+- `sudo fdisk -l /dev/nvme0n1` (interpret physical order by sorting on Start)
+- `sudo blkid /dev/nvme0n1p1 /dev/nvme0n1p3 /dev/nvme0n1p4 /dev/nvme0n1p5`
+
 KEEP (do not format):
 - /dev/nvme0n1p1 (EFI vfat) UUID=94CC-9DA4 (~99MiB, FAT32, mounted at /boot/efi)
 - /dev/nvme0n1p2 (MS reserved) (~15MiB)