I confirmed that I can create a squashfs larger than 2GB (used 2.1GB), then append a file to it (used a 50MB file) and the resulting squashfs can be unpacked just fine.

```
root@xenial-32:~# dd if=/dev/urandom of=big bs=10M count=210
210+0 records in
210+0 records out
2202009600 bytes (2.2 GB, 2.1 GiB) copied, 147.973 s, 14.9 MB/s
root@xenial-32:~# mksquashfs big big.squashfs
Parallel mksquashfs: Using 8 processors
Creating 4.0 filesystem on big.squashfs, block size 131072.
[==========================================================================================================================================/] 16800/16800 100%

Exportable Squashfs 4.0 filesystem, gzip compressed, data block size 131072
	compressed data, compressed metadata, compressed fragments, compressed xattrs
	duplicates are removed
Filesystem size 2150400.52 Kbytes (2100.00 Mbytes)
	100.00% of uncompressed filesystem size (2150465.88 Kbytes)
Inode table size 353 bytes (0.34 Kbytes)
	0.52% of uncompressed inode table size (67282 bytes)
Directory table size 21 bytes (0.02 Kbytes)
	84.00% of uncompressed directory table size (25 bytes)
Number of duplicate files found 0
Number of inodes 2
Number of files 1
Number of fragments 1
Number of symbolic links  0
Number of device nodes 0
Number of fifo nodes 0
Number of socket nodes 0
Number of directories 1
Number of ids (unique uids + gids) 1
Number of uids 1
	root (0)
Number of gids 1
	root (0)
root@xenial-32:~# dd if=/dev/urandom of=small bs=10M count=5
5+0 records in
5+0 records out
52428800 bytes (52 MB, 50 MiB) copied, 3.5235 s, 14.9 MB/s
root@xenial-32:~# mksquashfs small big.squashfs 
Found a valid exportable SQUASHFS superblock on big.squashfs.
	Compression used gzip
	Inodes are compressed
	Data is compressed
	Fragments are compressed
	Xattrs are compressed
	Fragments are present in the filesystem
	Always-use-fragments option is not specified
	Duplicates are removed
	Xattrs are stored
	Filesystem size 2150400.52 Kbytes (2100.00 Mbytes)
	Block size 131072
	Number of fragments 1
	Number of inodes 2
	Number of ids 1

Parallel mksquashfs: Using 8 processors
Scanning existing filesystem...
Read existing filesystem, 1 inodes scanned
Appending to existing 4.0 filesystem on big.squashfs, block size 131072
All -b, -noI, -noD, -noF, -noX, no-duplicates, no-fragments, -always-use-fragments,
-exportable and -comp options ignored

If appending is not wanted, please re-run with -noappend specified!

Recovery file "squashfs_recovery_big.squashfs_256" written
If Mksquashfs aborts abnormally (i.e. power failure), run
mksquashfs dummy big.squashfs -recover squashfs_recovery_big.squashfs_256
to restore filesystem

[==============================================================================================================================================-] 400/400 100%

Exportable Squashfs 4.0 filesystem, gzip compressed, data block size 131072
	compressed data, compressed metadata, compressed fragments, compressed xattrs
	duplicates are removed
Filesystem size 2201600.58 Kbytes (2150.00 Mbytes)
	100.00% of uncompressed filesystem size (2201667.49 Kbytes)
Inode table size 388 bytes (0.38 Kbytes)
	0.56% of uncompressed inode table size (68898 bytes)
Directory table size 40 bytes (0.04 Kbytes)
	80.00% of uncompressed directory table size (50 bytes)
Number of duplicate files found 0
Number of inodes 3
Number of files 2
Number of fragments 1
Number of symbolic links  0
Number of device nodes 0
Number of fifo nodes 0
Number of socket nodes 0
Number of directories 1
Number of ids (unique uids + gids) 1
Number of uids 1
	root (0)
Number of gids 1
	root (0)
root@xenial-32:~# ls
big  big.squashfs  small
root@xenial-32:~# mkdir a
root@xenial-32:~# cd a
root@xenial-32:~/a# unsquashfs ../big.squashfs 
Parallel unsquashfs: Using 8 processors
2 inodes (17200 blocks) to write

[==========================================================================================================================================|] 17200/17200 100%

created 2 files
created 1 directories
created 0 symlinks
created 0 devices
created 0 fifos
```