The short answer is that you should be safe if both
/dev/sdd3 were not changed by anything else inbetween your two
dd will copy data in blocks of 512 bytes which is the standard sector size of a hard drive (See Note 1). This means that if you stopped dd early it will have stopped after trying to write a whole sector of the hard drive. Under no circumstances does dd write something to disk and then change it. So if you stop early then nothing will have changed because the last thing dd did before stopping was to ask the OS to send a whole sector to disk.
In recent years many hard drives have been manufactured with 4096 byte sectors. The hard drives will report to the OS that they support 512 byte sectors and they will behave correctly if the OS tries to write 512 bytes. But to make this work the hard drive internally reads a 4096 byte sector, changes 512 bytes and then writes back the whole 4096 bytes. This will not cause corruption. But this will slow down your write speed. If you don't know what hard drive you have then you might want to set
bs=4096 just in case.